1. Field of the Invention
The present invention relates to a power transmission device for a vehicle.
2. Description of the Related Art
Japanese Patent Laid-open Publication No. H10-292827 (hereinafter referred to as “Patent Document No. 1”) discloses a driving force transmission device. The driving force transmission device includes a coupling unit as an example of an intermittent mechanism that is connected to a drive pinion shaft extending from a differential carrier accommodating a differential device as a power transmission mechanism. The coupling unit is arranged in an inside space of a cover fixed to one end of the differential carrier. The coupling unit is sealed up with oil by a coupling case, a shaft, an X ring and an O ring. The inside space of the cover is segmentalized into a fluid space (in detail, an air chamber) by a seal bearing, an oil seal and so on. The space in the differential carrier is enclosed with other oil lubricating the differential device through an oil seal etc.
Japanese Patent Laid-open Publication No. 2001-12507 (hereinafter referred to as “Patent Document No. 2”) discloses a coupling unit. This coupling unit is arranged in a front cover fixed to one end of a differential carrier, similar to the Patent Document No. 1. The front cover is enclosed, therein, with oil through oil seals. This oil different from the oil on the side of a rear differential as one example of the power transmitting mechanism flows and lubricates the inside of the coupling unit through an oil passage formed in a rotary case of the coupling unit